Improvement in hygrometers



UNITED STATES PATENT OEETCEo WILLIAM EDSON, OF BOSTON, MASSAQHUSETIS,ASSIGNOltTO SHEDI) 85 EDSON, OF SAME PLACE.

IMPROVEMENT IN HYGROMETERS.

Specification forming part of Letters Patent No. 48,620, dated July 4,1865.

To all whom it may concern:

Be it known that I, WILLIAM EDsoN, of Boston, county of Suffolk, andState ot' Massachusetts, have invented a Hygrometrical Index, the natureof which consists in a combination of pointers attached to a movablecenter and a diagram, all of which, in connection with a Masonshygrometer, or, as it is more commonly called, the wet and dry bulbhygrometer,77 will enable any one, by simple inspection of theinstrument, to ascertain the relative humidity and dew-point oi' theair, also the absolute amount of moisture in the air, without the aid oftables or calculation, and I do hereby declare that the following is afull and exact description of the same, which together with theaccompanying drawings and letters of reference marked thereon, willenable any one skilled in the art to make and use my invention.

In the drawings, Figure l is an elevation; Fig. 2, elevation ot' a partenlarged to full size; Fig. 3, section through S O.

A, B, and B iu Fig. l are the base and standard, made of any suitablematerial 5 W and D, two thermometers attached to the standard B and B.The bulb of the thermometer D is exposed to the air. That of WV isinclosed in silk, L, which is connected with and always kept moist bymeans of some strands of lampwick hanging into the water in the vesselF.

This instrument constitutes the well-known Mason hygrometer, which actsupon the principle that evaporation cools the body from which itevaporates, and, as has been found by experiment, this cooling is inproportion to the rapidity with which the evaporation proceeds, which,again, is in proportion to the dryness of the air in which theevaporation takes place. In other words, the lowering ofthe temperatureot the covered bulb is in proportion to the dryness of the air in whichit is placed.

K, Fig. 3, is a knob fastened to the stud S;

, S, stud, one end of which forms a center around which the points I t'swing; G, in all the tigures, a piece of wire, to which is attached thestud S; VV, guides, one ofwhich onlyis shown,

in which the wire G slides up and down; N,

spring for the purpose of holding the 'wire G in place and to bring uponit a gentle pressure, so that it, together with the stud S, the knob K,and pointers P I t', may stand in any position in which they may beplaced 5 P, in all the figures, a pointer permanently attached to thestud S. The use of this pointer is to enable the observer to adjust thestud S, around which the pointers I t' swing, to the mercury of thedry-bulb thermometer; I1', in all the figures, pointers permanently txedto the collet O, Fig. 3, and swinging with the collet C freely aroundthe stud S as a center; P', in Figs. l and 2, a small slide attached 4tothe pointer t', for convenience in adjusting the instrument to thewet-bulb thermometer.

It will be seen that the pointers I li are fixed in relation to eachother, and that one cannot move without the other. 'lhus in moving thepointer i to adjust it to the mercury ot' the wetbulb thermometer acorresponding movement is made'by the pointer I over the face of thediagram H H.

H H in Figs. l and 2 is a diagram containing lines and numbers whichindicate relative humidity, the dew-point, and absolute amount of wateryvapor in the air. The curved lines-n nearly horizontal-are drawn merelyfor convenience in making the dia-gram, and correspond to the linesindicating temperature on the dry-bulb thermometer. The curvedlinesnearly verticalare lines ot' equal relative humidity, and may betermed isohygrometrical lines,7 the numbers at .the upper end of theseare to be read as percentages ot' moisture*n that is, as relativehumidity. The lines running diagonally from leftdownto the right aredeW-pointlines. rlhenumbersuponthemunder the words dew-point7 indicatethe dew-point of the air when the pointer falls upon that line. Thenumbers in the vertical column at the right express the number of grainsof water (in the form ol" watery vapor) in the air corresponding to thedew-point.

In making an observation for the purpose ot' iinding the absolute amountof vapor, I adjust the instrument-thatis, arrange the pointers so that Ishall point to the mercury ofthe dry-bulb, and i to that ot' thewet-bulb-observe at which diagonal line the pointer I stands, followthis linedown, and the number in the vertical column at the right, towhich it runs, gives the number of grains of watery vapor in the air.This diagram, after all of the mechanical parts of the instrument arecomscale of figures and so constructed or 'drawn as to indicate therelative humidity of the air, the dew-point, and the absolute emountofmoistnre, either or all, When pointed out by an in dex Whose position isregula-ted by adjustment to the height of the mercury in wet and drybulb thermometers, substantially as and for the purpose set forth. Y

WILLIAM ED'soN.

Witnesses:

ABRAM BAILEY,

ISAAC KHARnIs.

